Recover the model parameters (active cells) from a set of physical property values defined on the entire mesh.

For a discrete set of model parameters \(\mathbf{m}\) defined on a set of active cells, the mapping \(\mathbf{u}(\mathbf{m})\) is defined as:

\[\mathbf{u}(\mathbf{m}) = \mathbf{Pm} + \mathbf{d} \,m_\perp\]

where \(\mathbf{P}\) is a (nC , nP) projection matrix from active cells to all mesh cells, and \(\mathbf{d}\) is a (nC , 1) matrix that projects the inactive cell value \(m_\perp\) to all inactive mesh cells.

The inverse mapping is given by:

\[\mathbf{m}(\mathbf{u}) = \mathbf{P^T u}\]
u(mesh.nC) numpy.ndarray

A vector which contains physical property values for all mesh cells.